The height of trees and the height of buildings

Auckland is a very leafy city. The trees that our forebears planted have slowly grown to maturity, resulting in many streets and suburbs with an attractive amount of greenery.

The city’s street trees are especially valuable… where they have been allowed to survive traffic engineering standards. For instance, there’s an immense difference in the look and feel of different parts of Symonds St. Areas around the university, with abundant, mature trees, feel much better than the concrete channel near the Wakefield St intersection.

But will development of taller buildings in residential neighbourhoods – three-storey townhouses and midrise apartments – erode Auckland’s leafiness? Will the buildings slowly grow above the trees, resulting in a landscape of roofs rather than a landscape of trees?

Evidence from other cities suggests that the answer is no. For example, Stu Donovan tells me that in Amsterdam street trees still rise above the midrise apartment blocks, creating leafy vistas.

To understand what might happen in Auckland as the city grows up, I’ve taken a look at the height of common street trees in New Zealand cities. Unfortunately, data on street trees in Auckland wasn’t easy to come by, but a PhD thesis by Fredericke Behrens provides some data on the abundance of different types of street trees in Christchurch. (“Selecting public street and park trees for urban environments“, Lincoln University, 2011)

Here’s a list of the ten most abundant street trees in Christchurch (Table 5-2 in the thesis), along with approximate mature heights (generally sourced from Wikipedia). Eight of the ten species have mature heights in the range of 15 metres or more, while three can grow up to 25 metres.

These species will generally be of a similar height as mid-rise apartment blocks, which may be in the range of 4-7 storeys high. Silver birches or ribbonwoods on the street can be attractive complements to medium-density development.

Species name

Origin

Mature height

Equivalent to:

Betula pendula (silver birch)

Exotic

15-25m

4-7 storeys

Quercus palustris (pin oak)

Exotic

18-22m

around 6 storeys

Fraxinus ornus (manna ash)

Exotic

15-25m

4-7 storeys

Plagianthus regius (ribbonwood)

Native

up to 17m

around 5 storeys

Cordyline australis (cabbage tree)

Native

up to 20m

6 storeys

Liquidambar styraciflua (sweetgum)

Exotic

15-21m

5-6 storeys

Prunus cerasifera ‘Nigra’ (black cherry plum)

Exotic

6-15m

2-4 storeys

Sophora tetraptera (kowhai)

Native

up to 15m

4 storeys

Quercus robur (English oak)

Exotic

15-25m

4-7 storeys

Prunus x Kanzan (Japanese cherry)

Exotic

8-12m

2-3 storeys

Furthermore, this list doesn’t include several less common species that play an important role in Auckland’s landscape, such as the London Plane tree, which usually grows to 20-30m (6-8 storeys) or even higher in exceptional circumstances:

In other words, it seems like we shouldn’t fear for Auckland’s leafiness: We can develop a lot more without eclipsing our trees. But that being said, I would argue that we need to do other things to preserve and improve our streets as we develop… such as planting more street trees.

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53 comments

Phil Goff has said that he wants a million more trees planted around Auckland. Good. At present Auckland is looking beautiful because of all the trees. Mainly planted by the city. In many of the new suburbs houses are close together and most have only a few shrubs and a small lawn. I think there are many public areas where more plants, from small ground cover ones to larger trees could be planted and then less costly mowing would be required.

I have to say I’ve never heard people complaining about intensification because of the impact of street trees!

Surely Rodney Hide’s evil in removing blanket tree protection across Auckland – as well as our refusal to build up, rather than out, leading to McMansions crammed onto small lots without space for a tree – has done a lot more harm!

Aucklanders planted trees without any rule requiring them, they kept trees without any rule requiring them. They became reluctant to plant large trees the day the Councils were stupid enough to introduce blanket tree protection. For weeks before it came in in my area you couldn’t get an aborist as they were all booked up cutting trees down. Trees that people might have voluntarily kept but chopped so they couldn’t be forced to keep them. It was a dumb rule that had the opposite effect of its intended purpose.

I have no doubt the perverse behaviour you mention occurred. However, at the time the law was changed back, there were thousands of trees growing across Auckland that suddenly had their lives cut short. Do you seriously believe that removing blanket tree protection has led to MORE trees in Auckland?

More than that. The planting of real street tree groves ended a long time ago. Auckland Transport don’t want to know about it. If we plant street trees,everywhere, the loss of trees to enable densification will be far less of an issue, if at all.

Agree, the idea of restricting people from chopping trees down on their own property is absurd. I would have thought the number of trees is reasonably closely proportional to amount of permeable land, therefore it is minimum permeable surface that should be dictated, which it already is for other reasons.

On a related subject I am keen to see more trees planted on in public space in my neighbourhood. When I walk around and look at berms with no trees (compared with the effect created by mature street trees) it makes me keen to advocate for a planting programme. It looks like the linked to thesis could be a good resource for that.

Sadly, the cutbacks on parks have meant that new trees are often planted shoddy, and not fixed even when called in. Our street had new trees planted some 3-4 years ago, and about 20 percent fell over because roots didn’t establish and the support struts fell apart… we can’t cut those budgets all the time. Less berm mowing, more tree care!

For a time while I lived in Flat Bush I spent time fixing the supports of some young trees and made them straight. I replanted many young plants which had been left on the ground. They were either pulled out by birds of hadn’t been properly planted by the gardeners One time I put a small bag of rubbish i found on the park into someones wheelie bin only to later see that the owner had taken it out and thrown it out on their own berm

Old photos of Auckland always look slightly weird due to the lack of mature trees. I guess the settlers probably preferred European trees so removed the whatever trees were left over after developing the city and replanted with exotics.

I do wonder what is going to happen to the berms and trees in areas zoned for intensification, such as New Lynn, when minimum parking requirements are also being lowered…Illegal parking. Does anyone know if there has been any effort to rethink how we could make better use of the existing road corridor?

Have a mix of species in a street is best practice these days. The point is that the next Dutch elm disease or similar that targets one species will only kill some of the trees on a street rather than every single one.

The more trees the better. Who cares if taller buildings come along. Just need to lower the speed limits, otherwise the trees are an unforgiving hazard to speeding drivers. The Manukau City Council parks team had a huge spend up in Manukau planting so many trees all over the place before their department got wiped out. Half the trees have died or have been ripped out and many are planted right under power lines, but I guess they will start to look ok in a few decades. I don’t actually know what kind of trees they are. Some random natives, but I much prefer deciduous over our natives.

I was being flippant. AT doesn’t want street trees because they are “non frangible” or whatever the term is, but has no problem allowing concrete/timber electricity poles that are just as tough if not tougher than street trees. If safety was a real issue they wouldn’t allow them (or concrete boundary walls/fences). No street tree is as strong as a concrete electricity pole. I’d rather crash into a pohutukawa.

yes trees are good. But for Orakei Local Board to give out 2000$ per tree to owners of significant trees seems like a huge waste of money. Not like Orakei people don’t have a spare couple of grand to take care of their trees…

Guess it depends if the native tree nazis get involved (since a lot of NZ councils now have a policy of planting natives in most situations). In urban environments typically deciduous tree’s work best (shade in summer, let the sunlight through in winter – which has the effect of cooling the city in summer and warming it in winter) however most native tree’s aren’t deciduous. They’re great for larger spaces like parks and Pohutukawa’s around beaches etc but not so much lining streets.

Deciduous trees have their own problems. Their leaf load is a major problem for drainage systems and for footpath cleaning and maintenance. Many popular species have roots that spread near the surface, causing expensive damage to roads and paths.

The point is to put the right tree in the right place. And that will differ depending on the context. (Height, vegetation, shape, footprint, root system, danger to errant road users, etc.)

In terms of Amsterdam, yes it’s a very green city — at least once you get beyond the older central city area. And the street trees are generaly beautiful. Here’s my street, for example, which has lots of beautiful street trees.

In some ways Amsterdam is a greener city than Auckland, notwithstanding the former’s higher density, because the streets incorporate high quality green elements. In comparison, most streets in Auckland are dire.

I support comments made by people above with regards to increased OPEX for parks. I really think that investing in freely available public spaces is an important way of building civic pride.

You may get a small sniffle. I take the maximum dose of anti-histamines and get daily nose bleeds over the worst week and weekly for about four months from torn sinuses. And not a nose bleed that spots, it literally pours out without dripping.

HSB1 while you are busy curdling the milk of human kindness you might like to reflect on the recent deaths during the thunderstorm in Melbourne. Many of the people affected by the charged rye pollen didn’t know they had an allergy. So maybe privet or silver birches might just cause you problems one day.

Peter I don’t think traffic engineering standards have ever been the major driver for removing trees in Auckland. A few get removed and because they are in public areas they get noticed. The real driver for removing trees in Auckland has always been intensification. People on large sections were more than happy to have a tree in their yard. But when the developer arrives to build infill or apartments the trees have to go.

For what it is worth my advice on the list of trees is you should never plant the following: silver birches as they are an allergen; cabbage trees as they will tangle in your mower and line trimmer and cost you a fortune; liquidambars due to the sharps things they drop that will hurt bare feet; willows will block your drains and now have an aphid that makes them go black and attract wasps; kowhai due to poisonous seeds and most important of all Pohutukawa as they only give a couple of weeks of show but look dark and gloomy and will inevitably be protected by some twit in the future so you risk being stuck with it. Plant a gleditsia for looks or a ginkgo for slow growth or a virgilia for native birds.

I do enjoy the amalgamation of building and tree/bushland. This – to me – seems alive and well in Auckland City. I do not think trees versus buildings is in any way an issue (in respect of relative height). Good husbandry and practical perspectives do the job without laws, sanctions or draconian measures. Interesting (to me) that my first stay in Auckland as a teenager attending University and (then) keen camera addict back in 1968. I was overawed by the sheer beauty of the Pohutuhawa flowers growing unabashedly streeet-side in the Mount Albert area and photographed many of them. So I guess all I want to point out is that beauty and balance can be found anywhere you look. I tend to look…

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